Field of the Invention
The present invention relates to the determination and generation of models and/or other augmentation information that may be used to support high-precision position, velocity, and/or timing (PVT) solutions based on signals received from overhead assets such as satellites and, in particular, to techniques suitable for providing such PVT solutions without resort to a generally proximate, terrestrial ground station with a fixed and precisely known position and/or networks of fixed ground stations.
Description of the Related Art
Radio signals have been used as an aid to navigation and to obtain position estimates for decades. In much the same way that sailors could navigate near land using two or more light houses, the earliest systems used a directional antenna that determined a bearing to two or more radio transmitters. As long as line of sight could be maintained between the receiver and the two or more radio transmitters, a location of the receiver could be determined by triangulating the known locations of the two or more radio transmitters and the bearings to each of those radio transmitters. And although this approach may generally provide just a horizontal location (latitude and longitude) of the receiver, this may be adequate for localized navigation, such as the landing of aircraft or the navigation of ships around nearby navigational hazards.
Limiting radio navigation systems to local two-dimensional positioning, however, does not address many interesting positioning problems. For example, surveyors often desire to know the height/altitude of a location as well as its latitude and longitude, and pilots of aircraft often desire to know their altitude. To address these desires, more complex and longer distance radio navigation systems are typically utilized. Many of these radio navigation systems rely on the basic principle that radio waves generally propagate through the air at a known speed. By measuring the length of time it takes for a radio wave to propagate between a transmitter and a receiver, a distance between the transmitter and the receiver may be determined. By using the distance between the receiver and several transmitters with known locations, it is possible to determine the position of the transmitter by trilateration. For example, by using three transmitters, it is possible to determine the latitude, longitude, and altitude of the receiver. As additional transmitters are used and detected by the receiver, additional variables may be removed from the solution. For example, by adding time information to the radio signals, a fourth transmitter may be used to solve for the current time at the receiver.
Global Positioning Satellite (GPS) navigation, and more broadly Global Navigation Satellite System (GNSS) navigation, has become the standard for most military and civilian radio navigation applications. There exist in both military and civil sectors hundreds of millions of GPS or navigation receivers that are used daily to provide real-time positioning and navigation. Many of these navigation receivers are associated with sophisticated communication devices such as cellular phones and/or smart phones. The GPS system is based on a constellation of approximately 24 to 32 middle-earth orbit (MEO) satellites that broadcast continuous carrier wave signals. A GPS receiver typically relies on the ability to receive signals from four or more satellites allowing the receiver to determine latitude, longitude, altitude, and time error at the receiver. A typical navigation receiver relying primarily on signals from GPS satellites may generally achieve positional accuracy to within about 10 meters.
Higher precision PVT solutions for a navigation receiver typically require an augmentation to the general GNSS infrastructure. Traditional augmentation approaches for satellite navigation techniques include real time kinematic (RTK) and precise point positioning (PPP) techniques that are commonly used in high accuracy agricultural, industrial, and timing applications. In a typical RTK system, a base station is installed in a fixed and known location. Once the base station is able to obtain a PVT solution from the satellite transmissions, it is able to transmit any differences between its known location and the PVT solution as a correction signal to a nearby mobile or roving unit. RTK systems are typically fairly expensive, require time to set-up the base station, and the base station and mobile unit need to stay within a close proximity to each other. In a typical PPP system, a network of fixed reference stations receive the satellite signals and generate correction information that is distributed to the navigation receiver using satellites or other terrestrial-based wireless technology, such as a cellular network. While less expensive than RTK systems, a navigation receiver in a PPP system generally takes up to 30 minutes to converge on a high precision PVT solution and provides poor coverage at high latitudes or in challenging environments such as cities, steep terrain, and heavily wooded areas.
Improved techniques are desired.